God’s benison go with you; and with those
That would make good of bad, and friends of foes!

– William Shakespeare

Macbeth, Act 2, Scene 4. The Old Man bids God’s blessing on Ross and Macduff, and all those who make good things out of bad and friends out of enemies. This echoes the Witches’ saying at the beginning of the play, “fair is foul; foul is fair.” The Old Man’s words appear to be warning Ross and Macduff to beware of Macbeth, that Duncan was killed by someone who was believed to be a friend but was in reality a foe. This fits in with the appearance vs reality them in Macbeth.